The invention relates to a diesel-electric drive system.
A drive system of this generic type is disclosed in the publication entitled “Energy Efficient Drive System for a Diesel Electric Shunting Locomotive”, by Olaf Koerner, Jens Brand and Karsten Rechenberg, printed in the “EPE'2005” Conference Proceedings, of the EPE Conference at Dresden between Sep. 11 and 14 2005. This publication compares two diesel-electric drive systems having a permanent-magnet synchronous generator with one another. These two drive systems differ only in that the generator-side converter of the voltage intermediate-circuit converter is a diode rectifier on the one hand and a self-commutated pulse-controlled converter on the other. The self-commutated pulse-controlled converter is referred to in this publication as an IGBT rectifier. In both drive systems, a braking resistor can be connected to the intermediate circuit of the voltage intermediate-circuit converter. A thyristor which can be turned off is provided for this purpose, and is also referred to as a gate turn-off thyristor (GTO thyristor). By means of this pulse impedance the DC voltage in the intermediate circuit of the voltage intermediate-circuit converter, supplies energy to the intermediate circuit in the braking mode, that is to say the load, in particular a rotating-field machine, thus ensuring that the maximum permissible intermediate-circuit voltage is not exceeded. A portion of this braking power can also be used to compensate for the drag torque of the idling diesel engine. This has the disadvantage that a further converter bridge arm must be used for the braking controller, and the additional rail system for this braking controller must be provided with the intermediate-circuit rail system. Depending on the braking power, it is possible that further converter bridge arms must be used for the braking controller.
In addition, a control apparatus is required for the braking controller.
DE 102 10 164 A1 discloses an apparatus for multiple rectifier feeding of a permanent-magnet synchronous motor in a power station. This permanent-magnet synchronous generator has two polyphase stator winding systems with different numbers of turns. One winding system is connected to a controlled rectifier, for example an IGBT rectifier. The purpose of this controlled rectifier is to regulate the power output and thus the rotation speed of the permanent-magnet synchronous generator. For this purpose, in the range of low rotation speeds, current flows and the electrical power thus flows exclusively via this winding system and thus via the controlled rectifier, which is connected to a DC voltage intermediate circuit. The second winding system is connected to an uncontrolled rectifier, for example a multipulse diode bridge, which is likewise connected to the same DC voltage intermediate circuit as the controlled rectifier. If the phase-to-phase rotation voltage (also referred to as the rotor voltage) is greater than the intermediate-circuit voltage of the DC voltage intermediate circuit, a current can flow in the second winding system and is rectified via the uncontrolled rectifier in the DC voltage intermediate circuit. In this case, because of the magnetic coupling between the first and the second winding system, the amplitude and phase angle of the current in the second winding system can be influenced by the current in the first winding system, which is regulated by the active rectifier (controlled rectifier). This means that the current in the winding system of the uncontrolled rectifier can also be regulated to a certain extent with the aid of the controlled rectifier. The majority of the real power transmitted by this apparatus is carried by the uncontrolled rectifier, thus allowing the controlled rectifier to be designed for a low power, and thus to be cost-effective. With the aid of this controlled rectifier, which is in general also referred to as a self-commutated pulse-controlled converter, heavily over-excited operation of the permanent-magnet synchronous generator is avoided. Furthermore, this compensates for harmonics in the generator torque, which are caused by the uncontrolled rectifier.
In the case of diesel-electric traction drives, for example diesel locomotives or mining trucks, the generator which is fitted to this engine is used to supply energy for the drive. The electrical voltage of the generator is kept at a constant intermediate-circuit voltage by means of the diode rectifier or the IGBT rectifier, from which intermediate-circuit voltage the load-side self-commutated pulse-controlled converter of the drive motors is supplied. During electrical braking, the power flowing in the voltage intermediate-circuit converter is precisely reversed. The energy is supplied through the load-side self-commutated pulse-controlled converter to the voltage intermediate circuit of the voltage intermediate-circuit converter. Since the diesel engine cannot absorb braking power, the braking energy must be converted to heat by means of a braking resistor. A voltage which is pulse-width-modulated by a brake controller is passed to a braking resistor for continuous power control.
This procedure has the disadvantage that, in the braking mode, the rectifier (diode or IGBT rectifier) remains unused, while the braking controller cannot be used in the traction mode. More power semiconductors than are necessary are therefore installed in the converter.
The problem is now to find a solution and a circuit in which the power semiconductors can be used both in the traction mode and in the braking mode without having to reconfigure the topology by means of circuit breakers in this case.
The invention is based on the discovery that, particularly at high power levels, the important factor is not the number of power semiconductors but their installed power or chip area. Particularly at high power levels, the power semiconductors are connected in parallel.